Regarding all laser beams, but especially those for use in material processing applications, the two main beam parameters which a user may need to measure are the total beam power and the spatial profile of the beam. Total beam power is measured by means of a laser power meter, of which many kinds exist in the market. A laser beam profiler measures the spatial irradiance distribution of the laser beam in order to characterize the beam. Beam parameters of interest include diameter, peak position, centroid position, beam uniformity. Other derived beam parameters include angular divergence and M2 beam propagation ratio.
A conventional method of measuring a laser beam profile with a camera involves attenuating the laser beam by many orders of magnitude, and allowing it to impinge directly on the focal plane of a camera, the attenuation bringing the incident radiation down to the measurement range of the camera. As an alternative, a beam splitter or output coupler can be used to couple out a small portion of the beam, which is then directed into the camera. Another method of measuring a laser beam profile with a camera involves directing the laser beam onto a diffuse scatterer, and measuring the image at the surface of the diffuse scatterer with a camera. With all of these methods the beam is measured only at the position of the camera focal plane or the plane of the beam output coupler or scatterer. The camera generates an analog or digital video output, and a data acquisition system records the camera video for processing, analysis, display, or the like.
For high power laser beams, such methods may be impractical or difficult to implement because the high power beam, in the case of beam profile measurements, may damage the optical attenuator, beam splitter/output coupler or diffusion screen, and in the case of power measurements, may damage the beam absorber surface.
In the article entitled “Laser Beam Characterization by Using Rayleigh Scattering” by K. C. Jorge et al., published in Annals of Optics, Vol. 5, XXVI ENFMC (Brazilian National Meeting of Condensed Matter Physics), May 2003, there is described a method of passing a focused laser beam through a chamber filled with an aqueous aniline solution to render the propagating beam visible by means of the Rayleigh scattering emitted laterally to the beam path. This laterally scattered light is imaged using a CCD camera, and the scattered intensity at points along the beam path, which is a representation of the beam intensity at those points, enables the value of M2 to be obtained.
However, the apparatus described in that article requires the use of a chamber filled with a liquid, which makes the apparatus cumbersome and complex to construct. Furthermore, that article does not mention or suggest how beam power could be measured.
There therefore exists a need for a system for measuring various characteristics of a laser beam which overcomes at least some of the disadvantages of prior art systems and methods.
The disclosures of each of the publications mentioned in this section and in other sections of the specification are hereby incorporated by reference, each in its entirety.